olivier13

en ce moment, l émission c dans l'air: le réchauffement s'accelere une question: laurent cabrol est il un sceptique notoire vis a vis du role de l'homme dans le réchauffement climatique?? en tout cas cette emission est assez interessante pour des néophytes regardez la...

bonjour a tous. je vais participer a une mission scientifique sur l'atoll de clipperton dans le pacifique est et je recherche une figure avec la trajectoire des cyclones dans la zone sur les cinquantes dernieres années (en gros). si qlq un sait ou je peut trouver ca... merci d'avance

ok seulement je croit que tu te trompe sur l'ampleur du phenomene decrit. les auteurs ont justement un probleme avec ce point. 1 on ne trouve pas de cratere d'impacte correspondant a cette "collision" donc on a pas affair a une collision classique. les auteurs évoque une comete et pas une meteorite qui aurait pu exploser avant d'atteindre le sol ou qui aurait bien atteint le sol mais sur la calotte de glace: donc pas de cratere. 2) les auteurs ne disent pas que cet impacte est la cause directe (ce qui remettrai en cause le role de la circulation océanique dans cet evenement climatique) mais que cet evenement a pu, en destabilisant ou en faisan fondre une partie de la callotte de glace, entrainer la modification de la circulation thermohaline qui semble incontestable pour cette période. oublions cette meteorite le YD est il un évenement global pour toi? et si oui alors question: si effectivement, la faune de clovis a disparu au moment du youger dryas, alors pourquoi les mammouths n ont ils pas disparu partout??? c'est un evenement global non?? je peut également t'assurer que l'on peut detecter le pic des essai nucléaire dans les années 70 partout sur la terre et pourtant la terre n'as pas entierement été vitrifié, ca se saurait le probleme est la. il n'est pas ici question d'une collision de type KT (limite crétacé tertiaire) qui provoque une extinction massive mais de qlq chose de plus réduit qui, par le biais de rétroaction (la circulation thermohaline) aurait pu modifier le climat. personne n'as dit que les mammouths avaient grillé sur place.

les extinctions ne sont pas forcement simultanées partout. je ne voit pas ou tu veux en venir.c'est ou tes "2000km de la"??

les articles de ce type sont payants.pour le reste je rectifierai la semaine prochaine.

je suis assez d'accord mais il y a un mais:on ne trouve que ce que l'on cherche: la mesure de l'iridium par exemple, il faut vraiment le vouloir et je ne pense pas que cet element ai jamais été mesuré dans les carottes de glaces. maintenant que l'on se pose la question ca sera peut etre fait. je suis egalement d'accord avec charlesmuller. il est difficile de trouver un lien de cause a effet entre cette meteorite et le YD étant donné la récurence d'evenements de cet type (DO) durant la derniere période glaciaire . c'est largement évoque dans realclimate (citation dans le premier message)

desolé mais je n'ai pas vraiment la foi de le traduire mais si certains points te posent probleme je peut essayer de t'aider...

bonjour a tous je lance un sujet de discussion a propos d'un article paru récemment (PNAS) a propos du younger dryas. les auteurs (il y en a beaucoup) de cet article on mis en evidence l'existence de dépots datant du YD sur tout le continent nord americain et qui contiendrait les traces d'un impacte meteoritique (microsperules, iridium, charbon...).les auteurs considérent que cet evenement pourrai etre a l'origine de la destabilisation de la calotte groenlandaise et nord americaine, entrainant par les apports d'eau douce dans l'atlantique nord, un ralentissement de la circulation thermohaline. abstract: A carbon-rich black layer, dating to 12.9 ka, has been previously identified at 50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at 12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at 12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggeringYDcooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America. conclusion: Our primary aim is to present evidence supporting the YD impact event, a major ET collision over North America at 12.9 ka, which contributed to the YD cooling, the massive extinction of the North American fauna, and major adaptations and population declines among PaleoAmericans. The unique, carbon-rich, YDB layer, coupled with a distinct assemblage of impact tracers, implies isochroneity of the YDB datum layer and thus highlights its utility for correlation and dating of the North American late Pleistocene. These associations, if confirmed, offer the most complete and recent geological record for an ET impact and its effects, such as global climate change and faunal extinction. This evidence also would represent a record of a major ET event having serious, widespread consequences for anatomically modern humans. que pensez vous de cet article. on trouve sur realclimate une critique de cet article :http://www.realclimate.org/index.php/archives/2007/10/younger-dry-as-dust/#more-478 "The Younger Dryas is so called because it corresponds, in the pollen record from Europe, to the latest (i.e. youngest) appearance of the Dryas octopetala pollen, an alpine flower in regions that are now far from alpine. It marks a clear period towards the end of the last ice age when the warming trend of the deglaciation in Europe particularly was interrupted for a period of about 1300 years before it got going again. There were clear glacier advances during this time and the moraines can be seen very clearly all around Europe and Scandinavia. The clues to what caused this remarkable, if temporary, turnaround have always lain in assessing its spatial extent, the exact timing and correspondence with other events. Two recent papers have shed some welcome and potentially controversial light on the subject. To appreciate those papers though, you need a little background. It is clear from the Greenland ice cores that the Younger Dryas was a huge event in that region - 10 to 15ºC cooling at Summit - and this is confirmed by studies of ocean sediments in the North Atlantic which also show large temperature drops (a few degrees) over this period. Particularly clear records of climate impacts are seen off Portugal and as far south as the Cariaco Basin off Venezuela. New evidence from proxy circulation tracers suggest that the North Atlantic overturning decreased significantly during the YD, possibly shutting down completely. This has all lent support to the theory, first suggested over a decade ago, that glacial meltwater interfered with the N. Atl. circulation causing an interruption of the ocean heat flow to the North. This is of course the prototype of the "ocean circulation changes imply a new ice age" meme which has been so hard to get rid of in recent years. But how far afield did this climate change reach? The event is been clearly seen in sediments off Santa Barbara (California) and in cave records from China, but both of these areas are still in the Northern Hemisphere, and exactly what is recorded (wind speed change and precipitation amounts?) is still a little ambiguous. But what about the south? The initial results from Antarctic ice cores at first seemed to show something very similar - the long warming through the deglaciation was interrupted by a cold reversal half way along. The relative dating was not very good at that time and it was quite plausible that the two events in Greenland and Antarctica were one and the same. When glacial advances in New Zealand were found to be around the same time, it seemed clear that the YD cooling had extended the entire length of the Atlantic! The only problem was that the favored mechanism, an ocean circulation change, no longer matched the data. Models of these shutdowns found it very hard (actually impossible) to get a cooling in the North and South at the same time. Lots of other ideas were suggested, but none that were really convincing. So scientists went on thinking that it probably was the ocean, but always with a bit of unease about the southern hemisphere results or the models. Clarity started to emerge when new techniques for lining up the ice cores in Antarctica and Greenland were developed. One technique used the very rapid changes in methane (which could be measured in both poles) to synchronise the chronologies. The thought being that methane changes are well mixed and so large changes in one hemisphere get transmitted very quickly to the other. With this came a big surprise - the Antarctic Cold Reversal started hundreds of years before the Younger Dryas! In fact, Antarctica stopped cooling just as the YD was getting started. This was evidence of a bi-polar see-saw in the ocean - something the models did seem happy to show. But what about the New Zealand glaciers? How did they fit in? There had been some loosely constrained pollen data that didn't show much cooling reported in 1999, but the result was still ambiguous. This is where the first of the new papers comes in. In it, Barrows et al show with improved dating that the New Zealand peak glacial advances actually were significantly younger than the YD. These dates seem more solid that the previous estimates and are supported by nearby ocean sediment evidence for a continued warming through the YD. So now that the southern hemisphere oddities have left the scene, does that mean we now have a full understanding of the event? Not quite. The ocean circulation theory has indeed been strengthened in recent years, but the search for a trigger continues - why did it happen when it did? As always, many ideas have been put forward - a shift in drainage pathways for Lake Agassiz from the Mississippi to the St. Lawrence, a solar trigger or a tropical Pacific trigger and now we have a brand new idea - a cometary impact. This has been suggested by a large group of researchers who have collectively been working on archaeological sites (Clovis) in North America and who noticed a layer of charcoal at about the same time as the YD at a number of disparate sites. They claim too that within this charcoal there is significant evidence of impact ejecta, and from this they suggest that the trigger for the YD was in fact an extraterrestrial impact. This doesn't really undermine the ocean mechanism - the comet is hypothesised to have caused significant meltwater to flow into the Atlantic and the ocean circulation changed as would be expected in the standard view. Some suggestions were made at meetings that the direct impact due to dust and smoke forcing from fires actually caused the initial YD cooling, but this doesn't seem quite as plausible (dust falls out of the air quickly). The researchers have however tried to link the impact with everything that was previously linked in time to the Younger Dryas - mammoth extinctions, the disappearance of the Clovis culture etc. - but it is very difficult to disentangle a direct consequence of an impact from the indirect consequence of the subsequent climate change. But these ideas are quite intriguing and they made quite a splash when announced in a coordinated session at AGU in the spring. There are three aspects of this work that will require independent confirmation to determine whether or not this is a viable explanation. Firstly, it should be possible to find the ejecta layer almost anywhere - peat bogs, lake sediment, ice cores etc. - wherever there is material of the right age. If that is indeed found (big if), then the first part of the hypothesis might be confirmed - that there was an impact at this time. The subsequent parts are much harder: depending on where any object landed or was centered, how can one show that it produced the meltwater that presumably caused the ocean circulation change? The source to the ocean of the meltwater (be it the Arctic, St Lawrence or Hudson Bay) has been unclear for many years. Finally, how can you show that the direct effect of the hypothesised comet was responsible for any impacts, rather than the indirect effect of the ocean change? These issues will, I suspect, take a long time to resolve. There are still some more YD mysteries though. The ocean models might have won the Southern Hemisphere round, but they still have a hard time explaining why it lasted so long, and how the rapid warming (10 or so degrees in the space of a few decades in Greenland) at the end occurred. The fact that similar events occurred all through the glacial period (Dansgaard-Oscheger events) implies that they must be fundamental to the climate system rather than a one off. An impact event doesn't impact those mysteries at all." bravo a ceux qui on pu lire jusqu'au bout

bonjour moi je suis étudiant en thése au cerege en paléoclimatologie/paléocéanographie

je trouve pas la video. quelqu un peut mettre le lien svp

c'est le 6 ou le 9 avril 1984?? faudrai savoir

merci a tous le probléme c'est que je doit impérativement récuperer toute l'eau de l'air que je préléve sinon il peut y avoir fractionnement isotopique et donc fausser la mesure. effectivement, je pense que je ne ferait que des prélevements ponctuels. je pense que le meilleur moyen est de refroidir fortement l'air pompé dans un tube en verrre enfin c'est un peu compliqué a décrire mais je vais devoir faire des plans .....

en fait je doit prelever 10ml d'eau dans l atmosphere et pas de calculer la teneur en eau et ceci afin de faire des mesures de la composition isotopiqque de cette vapeur

bonjour je travaille cet été a l'instalation et au suivie d'une station de mesure de l'évaporation en camargue pour le compte du CNRS. je doit également mettre en place un dispositif d'échantillonage de la vapeur d'eau. je pense savoir comment fabriquer ce type d'apareil mais bon peut étre que quelqu'un ici sait comment s'y prendre. donc si vous avez des info a me donner sur le sujet, elle seront bienvenu. merci

je suis a peu pres sur qu'il existe une voir deux series pollinique dans les vosges. je vais voir si je peux trouver qlq chose

pour info j'ai eu vent de l'élaboration d'un programme de recherche sur ce suget au CEREGE; y a il eu un lien entre climat et champ geomagnetique dans le passé??? en gros ce pourrait etre le titre de ce programme

j' ai vu ce type de phenomene depuis un avion au dessus des pays bas dans un champ d'eolienne avec des ondulation dans le brouillard plusieurs cetaines de metres sous le vent....

pour ceux que ca interesse: http://www.ncdc.noaa.gov/paleo/forcing.html on peut trouver ici ce que je cherchait merci charles.muller

merci je vais regarder ca en detail

je n'ai ni le courage ni le temps de relire tout le topic mais bon voila j'ai une question a poser. quelqu'un connait il une base de données qui recencerait les tephras ou les eruption majeurs sur des périodes longue (100 000 ans). je travaille sur une carotte provenant du nord de la papouasie nlle guinée et j'aimerais ajouter des time point dans mon modele d'age. merci d'avance

quelques flocons se battent en duel à saint cannat à 12 bornes à l'ouest d'aix

bonjour a tous. dans le cadre de mon master 2, je doit faire une étude sur le bilan hydrologique du bassin de l'arc (PACA) et son evolution sur les 30 dernieres années. je dispose pour cela de series de données sur les debits de l'arc à differents niveau ainsi que des precipitation journaliéres pour aix et rousset. j'ai pu remarquer que sur certaines périodes, les precipitations sur rousset sont plus importantes que sur aix et inversement(environ 15 km de distance). afin de verifier si cette différence est lié a des changement dans le type de flux global, je recherche des séries de données me donnnant la directions des vents en provence voir un indice qui permettrai de qualifier le type de flux sur la france (plutot océanique, plutot continental). $ merci d'avance pour votre aide

merci. trés utile ce site. sans indiscretions c'est quoi ton sujet de these?

le vent se renforce sur toute la cote med et dans les terre. tempete au sommet de l'aigoual