Dominique Jolly

Abrupt millennial climatic changes from Nussloch (Germany) Upper Weichselian eolian records during the Last Glaciation

Abstract Increasing attention has been focussed on the massive iceberg discharges in the North Atlantic, Heinrich events, during the Last Glaciation, and their worldwide terrestrial counterparts. However, these events are particular episodes among more regular cyclic events named Dansgaard–Oeschger events in ice cores or Bond cycles in marine cores. Here we examine grain size, δ13C, and magnetic susceptibility data from Nussloch, one of the most complete west European eolian sequence examined so far. These indices indicate that, during the 31–19xa0kyr interval (using chronology provided by radiocarbon, OSL and TL dates), millennial scale variations occurred affecting both precipitation and vegetation. Furthermore, these are associated with oscillations in the wind strength matching the dust deposition rate in Greenland, as recorded in the GRIP ice core. Our study shows that the abrupt climatic changes, the Dansgaard–Oeschger events, are also recorded in the west European loess sequences. This implies an atmospheric mechanism linking dust deposition over Greenland and Europe, which is probably connected to global climatic events during the Last Glaciation.

A Middle Miocene hominoid from Thailand and orangutan origins

The origin of orangutans has long been debated. Sivapithecus is considered to be the closest ancestor of orangutans because of its facial–palatal similarities, but its dental characteristics and postcranial skeleton do not confirm this phylogenetic position. Here we report a new Middle Miocene hominoid, cf. Lufengpithecus chiangmuanensis n. sp. from northern Thailand. Its dental morphology relates it to the Pongo clade, which includes Lufengpithecus, Sivapithecus, Gigantopithecus, Ankarapithecus and possibly Griphopithecus. Our new species displays striking dental resemblances with living orangutans and appears as a more likely candidate to represent an ancestor of this ape. In addition, it originates from the geographic area of Pleistocene orangutans. But surprisingly, the associated flora shows strong African affinities, demonstrating the existence of a temporary floral and faunal dispersal corridor between southeast Asia and Africa during the Middle Miocene, which may have played a critical role in hominoid dispersion.

Long‐distance pollen transport from North America to Greenland in spring

[1]xa0In the Arctic domain, there is evidence for very long distance transport of pollen grains from boreal forests to tundra environments. However, the sampling protocol used in earlier studies did not allow the determination of precise timing of the deposition of exotic grains. The ongoing “Epilobe” project monitors the deposition of exotic grains on the western and eastern coasts of Greenland utilizing wind filters, which are changed weekly throughout the entire year. A combination of the identification of tree pollen grains, the dates of deposition of the pollen on the filters, and the distribution map of the trees identified, allows the selection of modeled backward trajectories of air parcels responsible for the capture of the grains in the growing area of northeastern North America and their long-distance transport to Greenland. A survey of data obtained from four stations, analyzed during 2004 and 2005, indicates the occurrence of a general pattern every spring, which follows the main cyclone tracks reaching this Arctic region.

Long distance transport of pollen to Greenland

[1]xa0Four pollen traps were recently placed at coastal sites in East and West Greenland in order to assess long distance transport of pollen to the Arctic domain. By identifying potential vegetation source areas associated with air mass pathways we were able to produce the first detailed record of pollen transport from eastern North America to Narsarsuaq, southern Greenland. The record is based on observations and on a transport and dispersion model used to calculate back trajectories of the air masses. The evidence points to the pollen being transported northward by the air mass over Newfoundland and the Labrador Sea before reaching Narsarsuaq. At this point, the air mass was at an altitude of 3000 m. Deposition of pollen grains occurred with downward air movements associated with a 0.5 mm/h rain. The source areas for these pollen grains differ from those of dust and certain other aerosols that reach the summit of the Greenland Ice Sheet. The results demonstrate the need for continued maintenance and analysis of the Greenland pollen trap data in order to improve our understanding of atmospheric circulation and transport to high northern latitudes.

Quantitative reconstructions of annual rainfall in Africa 6000 years ago: Model‐data comparison

precipitation are based on 85 pollen sites 14 C dated at 6000 ± 500 years B.P and distributed over the whole of Africa. To improve the reliability of the pollen-based climate reconstruction, two methods are used: the ‘‘modern analogues technique’’ (MAT) and the ‘‘plant functional types’’ (PFT) methods. We then conduct a model-data comparison for five distinct regions, allowing an evaluation of model outputs (the Sahara-Sahel, the eastern Sahara, western equatorial Africa, East Africa, and Madagascar). The pollen-inferred reconstructions are compared with 21 mid-Holocene simulations yielded by Atmospheric General Circulation Models (AGCMs), and coupled ocean-atmosphere-vegetation models (OAVGCMs). The large-scale feature of the hydrological changes is shown to be well captured by most of the models. Data show that during the mid-Holocene, the Sahara was considerably wetter than today (+200 to +700 mm/yr). The results reinforce the conclusion that the AGCMs significantly underestimate this precipitation increase in the Sahara whereas the OAVGCM simulations are in accordance with the data. Our results show that vegetation and ocean feedbacks do not have a strong impact in the intertropical zone and that models fail to properly reproduce the climatic conditions in East Africa and Madagascar. The model-data comparison also suggests that the lengthening of the dry season during boreal winter in the west equatorial region is a robust feature although the pollen-based reconstruction shows no change or only slight drying there.

Pollen record of rapidly changing air trajectories to the North Pole

[1]xa0Tracing modern atmospheric dynamics is important for constraining models used in past climate reconstruction. However, these models must be verified by modern observations. We present the rapid changeover of two different air trajectories to the North Pole determined by studying the long distance transport of pollen. Samples were collected on a manned floating capsule drifting southward on the sea ice from the North Pole in 2002. It was observed that an air mass at 3000 m altitude transported birch and pine pollen released in Western Europe during week 22 (May 27). Two weeks later, during week 24 (June 10), alder, birch and willow pollen from eastern Siberia reached the drifting station with an air mass at 1000 m altitude. These particular patterns support independent investigations of air trajectories in the Arctic, especially the transport of anthropogenic pollutants such as sulfate and nitrate.

Maladie lupique, phénomène de Raynaud, cryoglobulinémie. Étude de 30 cas

Is Raynauds phenomena in systemic lupus erythematosus (S.L.E.) binding of the presence of cryoglobulinemia ? Thirty cases with SLE are studied : 66 % of the 15 cases with Raynauds phenomena have a cryoglobulinemia (freater than 150 mg/l) versus 40 % when Raynauds phenomena are absent. The group with cryoglobulinemia have a higher serum level of DS-DNA (p = 0,04).