Long‐term summer (AD751–2008) temperature fluctuation in the French Alps based on tree‐ring data     

CHRISTOPHE CORONA  JEAN‐LOUIS EDOUARD  FREDERIC GUIBAL  JOEL GUIOT  SYLVAIN BERNARD  ANDRE THOMAS  NICOLE DENELLE 《Boreas: An International Journal of Quaternary Research》2011,40(2):351-366

Corona, C., Edouard, J.‐L., Guibal, F., Guiot, J., Bernard, S., Thomas, A. & Denelle, N. 2010: Long‐term summer (AD751–2008) temperature fluctuation in the French Alps based on tree‐ring data. Boreas, 10.1111/j.1502‐3885.2010.00185.x. ISSN 0300‐9843. On the basis of a dense tree‐ring width network (34 unpublished multi‐centennial larch chronologies), this paper attempts to reconstruct, for the first time, the summer temperatures in the French Alps (44°–45.30°N, 6.30°–7.45°E) during the last millennium. The adaptative Regional Growth Curve standardization method is applied to preserve interannual to multi‐centennial variations in this high‐elevation proxy data set. The proxies are calibrated using the June to August mean temperatures from the last revised version of the HISTALP database spanning the period AD1760–2003 and adjusted to take into account the warm bias before 1850. About 45% of the temperature variance is reconstructed. Despite the use of the newly updated meteorological data set, the reconstruction still shows colder temperatures than early instrumental measurements between 1760 and 1840. The proxy record evidences a prolonged Medieval Warm Period persisting until 1500, with warm periods that resemble 20th century conditions but also cold phases before 1000 synchronous with Swiss glacier advances. The Little Ice Age is rather mild until 1660 if compared with other Alpine reconstructions. Thereafter, summers are 0.7 °C cooler than the 1961–1990 mean until 1920. The maximum temperature amplitude over the past 1250 years is estimated to be 3 °C between the warmest (810s, 1990s) and coldest (1810s) decades. Most of the 20th century is comparable with the Medieval Warm Period.  相似文献   

Solar irradiance during the last 1200 years based on cosmogenic nuclides   总被引：12，自引：0，他引：12  

EDOUARD BARD  GRANT RAISBECK  FRANÇOISE YIOU  JEAN JOUZEL 《Tellus. Series B, Chemical and physical meteorology》2000,52(3):985-992

Based on a quantitative study of the common fluctuations of ¹⁴C and ¹⁰Be production rates, we have derived a time series of the solar magnetic variability over the last 1200 years. This record is converted into irradiance variations by linear scaling based on previous studies of sun‐like stars and of the sun's behavior over the last few centuries. The new solar irradiance record exhibits low values during the well‐known solar minima centered at about 1900, 1810 (Dalton) and 1690 ad (Maunder). Further back in time, a rather long period between 1450 and 1750 ad is characterized by low irradiance values. A shorter period is centered at about 1200 ad , with irradiance slightly higher or similar to present day values. It is tempting to correlate these periods with the so‐called "little ice age" and "medieval warm period", respectively. An accurate quantification of the climatic impact of this new irradiance record requires the use of coupled atmosphere–ocean general circulation models (GCMs). Nevertheless, our record is already compatible with a global cooling of about 0.5‐1°C during the "little ice age", and with a general cooling trend during the past millenium followed by global warming during the 20th century (Mann et al., 1999).  相似文献   

The origin of Antarctic precipitation: a modelling approach   总被引：3，自引：0，他引：3  

GILLES DELAYGUE  VALÉRIE MASSON  JEAN JOUZEL  RANDAL D. KOSTER  RICHARD J. HEALY 《Tellus. Series B, Chemical and physical meteorology》2000,52(1):19-36

The contribution of different moisture sources to Antarctic precipitation for present‐day and glacial conditions is estimated with the NASA/GISS Atmospheric General Circulation Model. Despite its low horizontal resolution (8°×10°), this model simulates reasonably well the broad features of the observed present‐day hydrological cycle. Simulated present‐day Antarctic precipitation is dominated throughout the year by moisture from a subtropical/midlatitude band (30°S−60°S). The moisture supplied to a given coastal area of Antarctica originates mostly in the adjacent oceanic basin; closer to the pole, other oceanic basins can also contribute significantly. Replacing the present‐day sea surface temperatures (SSTs) and sea ice cover in the GCM with those from the CLIMAP oceanic reconstruction for the last glacial maximum (LGM), greatly increases the simulated latitudinal temperature gradient, with the consequence of slightly enhancing the contribution of low latitude moisture to Antarctic precipitation. It also changes the seasonality of the different contributions and thus their budget, particularly in coastal regions. Because the nature of LGM tropical SSTs is still under debate, we performed an additional LGM simulation in which the tropical SSTs are reduced relative to those of CLIMAP. The resulting decrease in the latitudinal gradient brings the relative contributions to Antarctic precipitation more in line with those of the present‐day simulation.  相似文献   

Origin of red beds in a Cambrian flysch sequence, Canadian Appalachians, Quebec     

JEAN LAJOIE  RÉ CHAGNON 《Sedimentology》1973,20(1):91-103

The basal unit of this flysch sequence consists of about 700 m of rhythmically interlayered red and green claystone intercalated with feldspathic sandstone and lithic conglomerate. Chemical analyses show that both types of claystones have approximately the same Fe₂O₃ content (8%). The presence within green claystone of inarticulate brachiopods, thin laminations of phosphate and pyrite, coupled with a high Mn content (Fe/Mn : 27) together with the composition of the chlorites, suggest that green mud was deposited slowly in a marine environment under reducing conditions. The hematite content of red claystone averages 4%. The Fe/Mn is high (71), and the clay fraction contains chamosite in addition to chlorite and illite. These characteristics favour a paralic oxidizing environment for the red muds. Rapid resedimentation of red sediment from a paralic environment into the green lithotope, rather than a lateral variation of facies, is suggested by: (1) the distribution of the two hemirhythms in the stratigraphic column, (2) the presence in the red hemirhythm of large slump structures, contorted laminations, and pebbly claystone, and (3) by the internal sedimentary structures of the coarse fraction.  相似文献   

Solute transport and water content measurements in clay soils using time domain reflectometry     

MAGNUS PERSSON  RONNY BERNDTSSON  SLAH NASRI  JEAN ALBERGEL  PATRICK ZANTE  YUKI YUMEGAKI 《水文科学杂志》2013,58(6):833-847

Abstract

Clayey and saline soils have been shown to be problematic for time domain reflectometry (TDR) measurements. This study presents some of these problems and discusses solutions to them. Thirteen solute transport experiments were carried out in three undisturbed soil columns of swelling clay soil from Tunisia, labelled S1, S2, and S3 respectively. The columns were collected at three different physiographical regions within a catchment. Water fluxes ranged from 1.2 to 7.2 cm day^?1. The large solute transport heterogeneity and large tailing indicated that preferential flow was most pronounced in S1. The preferential flow took place in voids between structural elements and in wormholes. In S3, preferential flow was also evident, but not to the same extent as in S1. In S2, the solute transport was more uniform with little preferential flow. The heterogeneity of the solute transport increased with the water flux in S1 and to a smaller extent in S3, whereas it remained constant in S2. In a previous dye experiment in the field, preferential flow in cracks was observed at those sites where S1 and S3 were collected. In the column experiments, preferential flow in these cracks was less due to the higher initial water content compared to the dye experiments, indicating that the desiccation cracks were closed by the swelling clay.  相似文献   

Chemical effect of carbonaceous aerosols on the diurnal cycle of MBL ozone at a tropical site: measurements and simulations     

CHATRAPATTY BHUGWANT  HÉLÈNE CACHIER  PHILIPPE BREMAUD  STÉPHANE ROUMEAU  JEAN LEVEAU 《Tellus. Series B, Chemical and physical meteorology》2000,52(5):1232-1248

During late austral summer and winter 1998, black carbon (BC) aerosols were monitored with an Aethalometer at 2 sites of La Réunion Island (Indian Ocean): Saint‐Denis, the main city and Sainte‐Rose, a quite uninhabited region situated at the east coast. BC concentration data at Saint‐Denis show a marked diurnal cycle, which may be primarily attributed to traffic. The background data found at night‐time display average BC concentrations, ranging from about 80 to 250 ng/m³ whereas during the day, BC concentrations increase by a factor of at least 4. In comparison, BC concentrations vary in the range of 10 to 60 ng/m³ at Sainte‐Rose. Ozone concentration was also measured at Saint‐Denis using a Dasibi photometer and found to be at significant levels (means: 16.5–23 ppbv in April and 28.5–34 ppbv in September). A noticeable increase of ozone concentrations during the day points out the build‐up of pollutants enhancing photochemical transformations. However, during traffic pollution peaks, ozone concentration displays systematic depletion. The comparison of ozone and BC measurements at both seasons points to some possible effects of heterogeneous interaction of ozone and its precursors with BC particles. These interactions were also simulated with a 0D time‐dependent chemistry model using conditions of a polluted site. The measured ozone concentration characteristics (mean concentration and range of variation) are well simulated in the presence of BC. Our model results show that at La Réunion Island adsorption of ozone and its precursors onto BC aerosol particles could be one of the important steps determining ozone concentration characteristics, especially in absence of photochemistry during night‐time.  相似文献   

Plio-Pleistocene rodent biostratigraphy and palynology of the Bresse Basin, France and correlations within western Europe     

JEAN CHALINE  GENEVIèVE FARJANEL 《Boreas: An International Journal of Quaternary Research》1990,19(1):69-80

Five new palynological sequences in the Bresse valley (France), covering Reuverian, Praetiglian, Tiglian and Eburonian-Waalian times, yielded rodent teeth of the Mimomys occitanus-savini lineage evolving in Eurasia by phyletic gradualism. For the first time the west European palynological zonation is correlated with the Eurasiatic rodent one, leading to the following attributions: Mimomys occitanus: Reuverian; Mimomys polonicus : Praetiglian to early Tiglian; Mimomyspliocaenicus : Tiglian; Mimomys ostramosensis: Eburonian to early Waalian; Mimomys savini occurring from Waalian to Cromerian. As a result, the Neogene biozones MN15 to MN17 can be defined by nine new subdivisions.  相似文献   

Analysis of a Sahelian annual rainfall index from 1896 to 2000; the drought continues     

YANN L'HÔTE  GIL MAHÉ  BONAVENTURE SOMÉ  JEAN PIERRE TRIBOULET 《水文科学杂志》2013,58(4):563-572

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Kilometre‐scale sand injectites in the intracratonic Murzuq Basin (South‐west Libya): an igneous trigger?     

JEAN FRANÇOIS GHIENNE  ANDREW HURST 《Sedimentology》2012,59(4):1321-1344

Mount Telout, situated at the edge of the Murzuq Basin, is a 325 m high conical hill within a circular collapse structure that records 0·5 km³ of sand intrusion into Silurian shales. Based on a comparison with other similar circular collapse structures around the Murzuq Basin, it is argued that sand injection in the form of pipes occurred during the Devonian. The overpressures triggering the process are inferred to result from a combination of: (i) tectonic uplift at a basin scale that initially focused regional ground water flows; and (ii) igneous intrusion within the sand‐rich Cambrian–Ordovician strata. The palaeorelief buried under the regionally extensive Silurian shales may have locally focused overpressures and localized sand injection at the 1 to 10 km scale. The Mount Telout injected sandbody and related features offer exceptional, seismic‐scale outcrop analogues for sand injections that are often identified in seismic reflection data. Large‐scale sand injections might be essential in petroleum exploration of the North African Lower Palaeozoic basins as they form seal‐bypass systems.  相似文献   

Evidence for carbonate platform failure during rapid sea‐level rise; ca 14 000 year old bioclastic flow deposits in the Lesser Antilles     

JESSICA TROFIMOVS  JODIE K. FISHER  HEATHER A. MACDONALD  PETER J. TALLING  R. STEPHEN J. SPARKS  MALCOLM B. HART  CHRISTOPHER W. SMART  GEORGES BOUDON  CHRISTINE DEPLUS  JEAN‐CHRISTOPHE KOMOROWSKI  ANNE LE FRIANT  STEVEN G. MORETON  MELANIE J. LENG 《Sedimentology》2010,57(3):735-759

Bioclastic flow deposits offshore from the Soufrière Hills volcano on Montserrat in the Lesser Antilles were deposited by the largest volume sediment flows near this active volcano in the last 26 kyr. The volume of these deposits exceeds that of the largest historic volcanic dome collapse in the world, which occurred on Montserrat in 2003. These flows were most probably generated by a large submarine slope failure of the carbonate shelf comprising the south‐west flank of Antigua or the east flank of Redonda; adjacent islands that are not volcanically active. The bioclastic flow deposits are relatively coarse‐grained and either ungraded or poorly graded, and were deposited by non‐cohesive debris flow and high density turbidity currents. The bioclastic deposit often comprises multiple sub‐units that cannot be correlated between core sites; some located just 2 km apart. Multiple sub‐units in the bioclastic deposit result from either flow reflection, stacking of multiple debris flow lobes, and/or multi‐stage collapse of the initial landslide. This study provides unusually precise constraints on the age of this mass flow event that occurred at ca 14 ka. Few large submarine landslides have been well dated, but the slope failures that have been dated are commonly associated with periods of rapid sea‐level change.  相似文献