Where to find 1.5 million year old ice for the IPICS “Oldest Ice” ice core

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice

Where to find 1.5 million yr old ice for the IPICS “Oldest-Ice” ice core

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice

Ajustements et ré-ajustements hydromorphologiques de cours d'eau à faible énergie dans un bassin versant sub-urbain consécutifs à des travaux historiques et une urbanisation récente.

International audienceThe EU Water Framework Directive (WFD, October 2000) mandated that the Member States of the European Union achieve the general objective of protection of aquatic ecology by 2015. European rivers and streams have to attain “good ecological status” through the preservation and restoration of aquatic environments. Member will have to ensure environmental continuity through “the adequate distribution of fish species and transport of sediments”. In France, more than 61,000 transverse structures – mill dams, weirs, diversion gates – have been identified on rivers as being obstacles to ecological and sedimentary continuity. Because of their historical occupation by societies, rivers flowing in the Paris area have long been anthropized and artificialized. River courses, channel shape, sediment transport and hydrological regime modifications have tremendously transformed the hydrosystems surrounding the city of Paris. The Merantaise’s catchment is one of this low energy river watershed, near Paris, that have been modified by historical engineering, especially during medieval-modern times and by the building of the Versailles Castle (XVIIth century). The hydraulic infrastructures are still there and impact the hydromorphogical conditions of the river (incision, lateral erosion, . . . ). In addition to these ancient pressures a rapid and massive urbanization of the suburban areas has applied a new type of constraint to the hydrosystems in recent decades. This undermines the balance that was established following ancient engineering and disturbs the current functioning of the valley. These new types of land occupation have significantly altered the ecological circumstances and transformed the hydrological responses of rivers. In this study, we therefore seek to understand these processes of successive adjustments (ancient and recent) of a small river from the urban margins of the Orge watershed (to the south of Paris). We use a multi-scalar spatial and temporal approach to reconstruct the hydromorphological circumstances ancient and current, by hydrological chronicles and archives documentation

Évaluation et significations de la douleur chez l’adolescent drépanocytaire

International audienc