North western Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France and possible relations with Mont-Blanc glaciers fluctuations

International audienceA 14-m long piston core was retrieved from Lake Le Bourget, NWAlps (France), in order to provide a continuous record of flooding events of the Rhone River during the Holocene. The selection of the coring site was based on high resolution seismic profiling, in an area with limited mass wasting deposits and accumulated proximal Rhone River inter-and underflow deposits. The age-depth model of this core is based on (i) 14 AMS radiocarbon dates, (ii)radionuclide dating(137Cs) and (iii) the identification of historical data (flood events, eutrophication of the lake).The sedimentary record dates back to 9400 cal BP, and includes a thin mass wasting event deposited around 4500 cal BP. A multi-proxy approach was used to track the evolution and origin of clastic sedimentation during the Holocene, in order to identify periods of higher hydrologic al activity in the catchment area. Spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals (especially the Illite crystallinity index) allowed locating the main source area of fine grained clastic particles settling at the lake after flood events. This dataset highlights up to 12 periods of more intense flooding events over the last 9400 years in Lake Le Bourget and shows that the main source area of clastic particles during this period is the upper part of the Arve River drainage basin. This part of the catchment area drains several large glaciers from the Mont-Blanc Massif, and fluctuations in Rhone River flood supply in Lake Le Bourget is interpreted as resulting essentially from Mont-Blanc Glacier activity during the Holocene.The comparison of clastic sedimentationin Lake Le Bourget with periods of increasing land use and periods of Alpine glacier and mid-European lake level fluctuations, suggest that the core LDB04 clastic record in Lake Le Bourget is a continuous proxy of the Holocene hydrologic al history of the NW Alps

Western Pacific atmospheric nutrient deposition fluxes, their impact on surface ocean productivity

The atmospheric deposition of both macronutrients and micronutrients plays an important role in driving primary productivity, particularly in the low-latitude ocean. We report aerosol major ion measurements for five ship-based sampling campaigns in the western Pacific from similar to 25 degrees N to 20 degrees S and compare the results with those from Atlantic meridional transects (similar to 50 degrees N to 50 degrees S) with aerosols collected and analyzed in the same laboratory, allowing full incomparability. We discuss sources of the main nutrient species (nitrogen (N), phosphorus (P), and iron (Fe)) in the aerosols and their stoichiometry. Striking north-south gradients are evident over both basins with the Northern Hemisphere more impacted by terrestrial dust sources and anthropogenic emissions and the North Atlantic apparently more impacted than the North Pacific. We estimate the atmospheric supply rates of these nutrients and the potential impact of the atmospheric deposition on the tropical western Pacific. Our results suggest that the atmospheric deposition is P deficient relative to the needs of the resident phytoplankton. These findings suggest that atmospheric supply of N, Fe, and P increases primary productivity utilizing some of the residual excess phosphorus (P*) in the surface waters to compensate for aerosol P deficiency. Regional primary productivity is further enhanced via the stimulation of nitrogen fixation fuelled by the residual atmospheric iron and P*. Our stoichiometric calculations reveal that a P* of 0.1 mu mol L-1 can offset the P deficiency in atmospheric supply for many months. This study suggests that atmospheric deposition may sustain similar to 10% of primary production in both the western tropical Pacific

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

Piston core record of Late Paleogene (31 Ma) to recent seafloor hydrothermal activity in the Southwest Pacific Basin

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94790/1/palo1386.pd

Dramatic Transcriptional Changes in an Intracellular Parasite Enable Host Switching between Plant and Insect

Phytoplasmas are bacterial plant pathogens that have devastating effects on the yields of crops and plants worldwide. They are intracellular parasites of both plants and insects, and are spread among plants by insects. How phytoplasmas can adapt to two diverse environments is of considerable interest; however, the mechanisms enabling the “host switching” between plant and insect hosts are poorly understood. Here, we report that phytoplasmas dramatically alter their gene expression in response to “host switching” between plant and insect. We performed a detailed characterization of the dramatic change that occurs in the gene expression profile of Candidatus Phytoplasma asteris OY-M strain (approximately 33% of the genes change) upon host switching between plant and insect. The phytoplasma may use transporters, secreted proteins, and metabolic enzymes in a host-specific manner. As phytoplasmas reside within the host cell, the proteins secreted from phytoplasmas are thought to play crucial roles in the interplay between phytoplasmas and host cells. Our microarray analysis revealed that the expression of the gene encoding the secreted protein PAM486 was highly upregulated in the plant host, which is also observed by immunohistochemical analysis, suggesting that this protein functions mainly when the phytoplasma grows in the plant host. Additionally, phytoplasma growth in planta was partially suppressed by an inhibitor of the MscL osmotic channel that is highly expressed in the plant host, suggesting that the osmotic channel might play an important role in survival in the plant host. These results also suggest that the elucidation of “host switching” mechanism may contribute to the development of novel pest controls

Soluble and insoluble lithium dust in the EPICA DomeC ice coreImplications for changes of the East Antarctic dust provenance during the recent glacialinterglacial transition

International audienceContinental dust impurities in Antarctic ice provide information on climate changes in the dust source areas and on past atmospheric circulation. We investigated records of dust species from the last 45 ka in the East Antarctic EPICA DomeC (EDC) ice core with special emphasis on the lithium (Li) content of dust. We obtained two complementary Li-records using a new Ion Chromatography (IC) technique in line with Inductively Coupled Plasma-Sector Field Mass Spectroscopy (ICP-SFMS). Concentrations of soluble Li (Li+) were obtained using IC, while total concentrations of Li (LiT) were obtained using ICP-SFMS, providing an ideal opportunity to investigate the soluble and insoluble chemistry of Li in East Antarctic dust over the last glacial–interglacial transition. The records show that changes in the solubility of Li are associated with climatic changes. For the late glacial period and the Antarctic Cold Reversal (ACR) a large fraction, up to 75%, of the LiT content is present as insoluble minerals whereas for the Holocene period it seems that Li is present mainly as soluble salts (Li+). We compared the concentrations of Li+ with the concentrations of Ca2+ and the mass and size characteristics of the dust, which were obtained using Coulter Counting (CC). Furthermore we compared the concentrations of LiT with the concentrations of BaT. Our analysis suggests that the changes in solubility of Li along the EDC ice core are related to changes in compositions of the dust minerals. During the late glacial period, changes in the dust composition is characteristic of variations in the strength of the atmospheric circulation, while changes over the last glacial–interglacial transition are indicative of a change in the major dust source areas. The dust characteristics for the glacial and the Holocene periods indicate two different dust types. The glacial dust type partly disappeared after the ACR, while the Holocene dust type appeared significantly after around 16 ka BP and became dominant after the ACR. The relative increase in the Holocene dust type at the glacial–interglacial transition could be due to changed conditions in the potential source area or to changed patterns of atmospheric circulation, resulting in enhanced transport from a source area that was different from the glacial source areas

Source variable of the Bourget Lake sediment between LIA and older sediments : climatic implications

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Signaux terrigènes dans les grands lacs subalpins : un marqueur régional à haute résolution des conditions paléo-hydrologiques ?

The Mid-to Late Holocene fluctuations in detrital input are recorded in the sediments of Lakes Constance and Bourget which are fed by two of the most important Alpine rivers : the Rhine and Rhône, respectively. The sediments in these lakes contain a mixture of autochthonous calcite and partly silici-clastic river-born material. Hence calcium (Ca) concentrations may be considered as inversely proportional to the detrital input. Eight Ca-depleted phases are recognised in Lake Bourget record over the last 7 200 years. Lake Constance record spans the last 5 000 years and exhibits five Ca-depleted phases, all of them being contemporaneous with the ones recorded in Lake Bourget. On a regional scale, those periods of enhanced detrital input correspond to phases of higher lake-level reported in Jura and French Prealps as well as advances in Alpine glaciers. Although they probably contain a hardly assessable anthropic part, the detrital input signals seem to be paced by Holocene changes in hydrological pattern. Disentangling the human-from the climate-trigered part of such signal will require further research in order to quantitatively reconstruct Holocene Alpine hydrology and climate.Les fluctuations holocènes de la décharge détritique du Rhin et du Rhône ont été enregistrées dans les sédiments des lacs de Constance et du Bourget, situés aux débouchés de leurs cours alpins. Dans ces deux lacs, le sédiment est constitué d 'un mélange de carbonate authigène et d'une fraction allochtone plus moins ou moins silicatée, en fonction de la nature du bassin versant. Dans ces conditions, la concentration en calcium ([Ca]) du sédiment peut être considérée comme inversement proportionnelle à la décharge détritique. Huit phases d'augmentation de la décharge détritique (baisse de [Ca]) ont ainsi été identifiées dans les sédiments du lac du Bourget. Dans ceux du Lac de Constance, cinq phases synchrones de celles du Bourget ont été documentées sur les derniers 5 000 ans. A l'échelle régionale, ces périodes de fort détritisme correspondent à des phases de haut niveau lacustre dans le Jura et les Préalpes françaises et d'avancées des glaciers dans les Alpes nord-occidentales. Les signaux sédimentaires détritiques des lacs subalpins contiennent très probablement une part difficilement quantifiable due aux activités humaines dans les bassins versants. Séparer les parts respectives des forçages climatique et anthropique dans ce type de signaux demeure un challenge pour mieux cerner à la fois l 'évolution des conditions hydrologiques holocènes et celle des modes d'occupation des sols depuis le Néolithique.Arnaud Fabien, Wessels Martin, Chapron Emmanuel, Revel-Rolland Marie, Desmet Marc. Signaux terrigènes dans les grands lacs subalpins : un marqueur régional à haute résolution des conditions paléo-hydrologiques ?. In: Collection EDYTEM. Cahiers de géographie, numéro 6, 2008. Du climat à l’homme, dynamique holocène de l’environnement dans le Jura et les Alpes. pp. 77-88

Signaux terrigènes dans les grands lacs subalpins : un marqueur régional à haute résolution des conditions paléohydrologiques ?

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